Re: [PATCH V4] file-posix: allow -EBUSY error during ioctl(fd, BLKZEROOUT, range) on block

[John Snow <jsnow@redhat.com>]

On 3/22/21 5:25 AM, ChangLimin wrote:
> For Linux 5.10/5.11, qemu write zeros to a multipath device using
> ioctl(fd, BLKZEROOUT, range) with cache none or directsync return -EBUSY
> permanently. Fallback to pwritev instead of exit for -EBUSY error.
> 
> The issue was introduced in Linux 5.10:
> https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=384d87ef2c954fc58e6c5fd8253e4a1984f5fe02
> 
> Fixed in Linux 5.12:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=56887cffe946bb0a90c74429fa94d6110a73119d
> 
> Signed-off-by: ChangLimin <changlm@chinatelecom.cn>

To be clear, when I asked "When do we get -EINVAL?" it wasn't because I 
doubted that we would ever get it, I was just unclear of the 
circumstances in which we might receive EINVAL and was hoping you would 
explain it to me.

> ---
>   block/file-posix.c | 8 ++++++--
>   1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/block/file-posix.c b/block/file-posix.c
> index 20e14f8e96..d4054ac9cb 100644
> --- a/block/file-posix.c
> +++ b/block/file-posix.c
> @@ -1624,8 +1624,12 @@ static ssize_t 
> handle_aiocb_write_zeroes_block(RawPosixAIOData *aiocb)
>           } while (errno == EINTR);
> 
>           ret = translate_err(-errno);
> -        if (ret == -ENOTSUP) {
> -            s->has_write_zeroes = false;
> +        switch (ret) {
> +        case -ENOTSUP:
> +            s->has_write_zeroes = false; /* fall through */
> +        case -EBUSY: /* Linux 5.10/5.11 may return -EBUSY for multipath 
> devices */
> +            return -ENOTSUP;
> +            break;

What effect does this have, now?

We'll return ENOTSUP but we won't disable trying it again in the future, 
is that right?

Kevin, is this what you had in mind?

--js

>           }
>       }
>   #endif
> --
> 2.27.0
>